What was in the note passed to Danny Alexander during the chancellor's spending review statement to the Commons on Wednesday? Did you clock the vignette, as Newsnight did? A fold of paper was handed along the government frontbench to the chief secretary to the Treasury, who opened it, read it, then promptly budged up behind George Osborne. Perhaps Danny was trying to ride in George's slipstream. Perhaps a spin doctor monitoring events had decided that even the affluent chancellor's shoulders weren't broad enough to carry the burden of obscuring his desperately compromised lackey from public view.

Admittedly, the contents of the note are not the greatest mystery of that day – but we shall come to how on earth it took a mere five months since the election before certain Liberal Democrats had assimilated so totally into the Tory party that they were walking on two legs and cheering the most misery-inducing cuts, even as the electorally suicidal nature of this position became clearer by the day.

When Jeremy Paxman asked about the missive, Danny affected to have forgotten what it contained. Allow me to float a theory. Last year, Stephen Fry wrote a published letter to his 16-year-old self – a sort of "if only you knew what I know now" exercise designed to offer reassurance and guidance to a floundering soul. Alas, though Fry's letter was typically charming, its popularity inspired considerably less eloquent public figures to pen their own versions, with everyone from Patsy Kensit to Simon Cowell offering their younger selves a hindsighted arm around the shoulders.

Clearly, the format needs refreshing – an end best achieved by means of a simple reversal. So may I suggest that on Wednesday, Danny Alexander was the first public figure to be in receipt of a letter from his younger self. Think of it as "out of the mouths of babes"; or rather, "out of the mouths of grownups who barely five months ago appeared in possession of at least the odd principle, but who have since embarked on a political journey of such staggering speed and distance that it makes the rightward lurches of some New Labour ministers now seem minuscule".

In this idle fantasy, what was being passed along the frontbench during Osborne's speech was a note not from the 16-year-old Danny Alexander, but from the Danny Alexander who roamed the Earth in early May 2010.

"Dear Danny," this letter from his younger and wiser self might begin. "As you read this, you are sitting next to the prime minister, while behind you MPs wave their order papers to salute painful cuts. Please take a moment to absorb the magic.

"In a minute George will sit down, and David and Nick are going to smirk and thump him on the back and stop just shy of ruffling his hair in what will look like a goal celebration as performed by the type of public schoolboys who don't really understand football. Danny, you disappoint me. Given that you're not the only former publicist in the government – the prime minister's only job outside politics was in PR – you might have managed the staging of today's announcement more tastefully. You could have got the chancellor to lift up his shirt to reveal a vest bearing the slogan, Just Did It.

"Later, you will tour the TV studios, where you'll repeatedly declare that you didn't get into politics to cut public spending. I hate to break it to you – you used to know this stuff – but you and the Liberal Democrats are enabling people who got into politics precisely for that reason, which is why the benches behind you were cheering.

"Tomorrow, the Institute for Fiscal Studies will explain in detail why your plans are regressive, and the deputy PM will be foolish enough to pronounce this 'distorted and a complete nonsense'. I honestly can't imagine it now, Danny, when people are warming to Nick and not David in the televised election debates. But by the time you read this, Cameron will insist on making joint appearances with Clegg, because they throw him into sympathetic relief.

"As for you, I must remind you that you have risen without trace. Five years ago, you were the press officer for the Cairngorms national park. This week, the Cairngorms launched the world's first national park iPhone app, and it's funny to think that had your life continued on that path, you would have spent today explaining how easy visitors would now find it to locate cafes and loos among the peaks. As it was, you passed it filling Osborne's water glass.

"You've come a long way, baby … Yours, regretfully, Danny."

Odd that people should eulogise hindsight, when principled foresight is a far more wonderful thing. Indeed, watching the week unfold, restless Lib Dems whose core beliefs have a rather longer half-life than Danny's must have reflected that the thing about selling out is that people tend to do it to gain something. Selling out to virtually guarantee his compadres a loss would seem an idiosyncrasy too far, even within a party as traditionally Bizarro as the Liberal Democrats.